1. Field of the Invention
The invention relates generally to liquid level controllers of the type used for automatic level control in oil field applications and the like and, more particularly, but not by way of limitation, it relates to an improved liquid level controller that is pollution free as it does not bleed control gas into the atmosphere.
2. Description of the Prior Art
The prior art includes numerous types of float-operated and pressure-operated switching arrangements for controlling the liquid level in field storage tanks of various types, particularly those that are used in the petroleum industry. A series of floatless controllers for use on inlet gas scrubbers for compressors is available from Kimray, Inc. of Oklahoma City, Okla. and this series of valves is identified as Type 100, 200 and 400 PLC Floatless Controllers. This type of controller may be applied to any liquid level control application in conjunction with a diaphragm-type motor valve. The same manufacturer also provides a Type PFS series float-operated pilot valve for use on oil and gas separators, water knock-outs, gas scrubbers, accumulators and related devices.
U.S. Pat. No. 2,882,724 is representative of a prior art type of liquid level metering apparatus. This patent teaches free float liquid metering utilizing a metering vessel containing a float member that is free to move up and down the column vessel between movable arms. The movable arms are each positioned to operate actuating assemblies which function to open and close the fluid inlet valve to the vessel and the fluid outlet valve.
U.S. Pat. No. 3,970,099 is illustrative of another type of liquid level controller wherein a vent valve reacts to movement of a float suspended within a container or vessel. A pneumatic vent valve responds to float movement through a simplified direct-acting mechanism having a sealed shaft between the float and vent chambers. Here again, we have a pneumatic control system that is particularly adaptable for allowing a compressor to be shut down when liquid level reaches a predetermined height. However, the device is also adaptable for use with pressure vessels, boilers and the like. The U.S. Pat. No. 4,573,489 is directed to a dump valve which includes a float/float arm sensor within a gas scrubber container. The liquid level responsive float is connected to operate a vent valve which, in turn, is connected to a small diaphragm spool valve that feeds through a pressure regulator unit. A sensitive, small pneumatic signal-responsive diaphragm spool valve is utilized in parallel with the float-operated vent valve so that when the vent valve is open due to rising liquid level, a small pneumatic control signal is delivered through the spool valve to a pneumatic control chamber on one side of a relatively large diaphragm of an automatic dump valve. This dump valve enables quick, manual operation whenever desired as an override to the automatically responsive condition.